I've been with Optus, then Telstra, and now Optus again. I'm not under contract but staying with Optus not because the service is fantastic, but because I'm worried switching will get me something worse.

Optus's customer service is alright. It's nice that you can contact people via live chat and not have to wait on the phone; they also used to have 24h service which is fantastic for night owls. I think they've since done away with it, though their service times are still fairly wide. Cust. service does try to help you, but it's pretty hard to improve a service by much if it's crap in your area.

Their prices are average, generally cheaper than Telstra (may vary, haven't checked for a while) but there are other providers around with aggressively-lower prices.

Unfortunately, the service itself leaves much to be desired. There are some periods of time when the internet is really slow; I suspect they might be oversubscribed, and/or the infrastructure in my area is pretty bad/outdated.

On the whole, Optus is alright but if you try something cheaper that works for you, I'd probably want to try that too.